Problema con grafico

Ciao a tutti.
Questo codice è stato generato da Geo Gebra. Fino ad oggi non mi ha mai dato problemi ma questo codice proprio non me lo accetta.

`
\documentclass[10pt]{article}
\usepackage{pgf,tikz}
\usetikzlibrary{arrows}
\pagestyle{empty}
\begin{document}
\definecolor{uququq}{rgb}{0.25,0.25,0.25}
\definecolor{qqqqcc}{rgb}{0,0,0.8}
\definecolor{qqzzww}{rgb}{0,0.6,0.4}
\definecolor{qqwwtt}{rgb}{0,0.4,0.2}
\definecolor{ttttff}{rgb}{0.2,0.2,1}
\definecolor{qqqqff}{rgb}{0,0,1}
\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1.0cm,y=1.0cm]
\draw[->,color=black] (-3,0) — (6,0);
\foreach \x in {-2,2,4}
\draw[shift={(\x,0)},color=black] (0pt,-2pt);
\draw (5.52,0.13) node [anchor=south west] { t};
\draw[->,color=black] (0,-5) — (0,9);
\foreach \y in {-4,-2,2,4,6,8}
\draw[shift={(0,\y)},color=black] (2pt,0pt) — (-2pt,0pt);
\draw (0.16,8.35) node [anchor=west] { v};
\clip(-3,-5) rectangle (6,9);
\draw (2.9,0.9) node[anchor=north west] {$t_{w}$};
\draw (4.48,0.96) node[anchor=north west] {$t_{p}$};
\draw[line width=0.4pt,dash pattern=on 3pt off 3pt,color=ttttff] plot[raw gnuplot, id=func0] function{set samples 100; set xrange [-2.9:5.9]; plot -0.55*x**2+0*x+8};
\draw [line width=0.4pt,dash pattern=on 1pt off 3pt on 6pt off 4pt,color=qqwwtt,domain=-3:6] plot(\x,{(–16-4.21*\x)/1});
\draw[line width=2pt,color=qqzzww] plot[raw gnuplot, id=func1] function{set samples 100; set xrange [0.1:3.6999999999999997]; plot -0.55*x**2+0*x+8};
\draw[line width=2pt,color=qqqqcc] plot[raw gnuplot, id=func2] function{set samples 100; set xrange [3.9:4.25]; plot -4.21*x+16};
\begin{scriptsize}
\fill (3.8,0) circle (1.5pt);
\draw (4.35,0)– ++(-1.5pt,-1.5pt) — ++(3.0pt,3.0pt) ++(-3.0pt,0) — ++(3.0pt,-3.0pt);
\fill (0,8) circle (1.5pt);
\draw (0.26,8.42) node {$D$};
\end{scriptsize}
\end{tikzpicture}
\end{document}
`
Vi allego il grafico in png
Grazie per l’aiuto a tutti
[attachment:1]1.4.png[/attachment]